Design and Analysis of a 94 GHz CMOS Power Amplifier Using Miniature Current Combiner

A four-stage eight-way power amplifier (PA) for 94 GHz image radar in 90 nm CMOS is reported. The PA comprises a common-source (CS) input stage, a CS first gain stage and a two-way CS second gain stage, followed by an eight-way CS output stage using miniature triple Y-shaped divider and combiner. Positive feedback is used at both the input and the first gain stages to enhance gain, which in turn leads to a higher output power (Pout) and power-added efficiency (PAE). At each branch’s input terminal, the triple Y-shaped current combiner can convert the serial RL load to the optimal load impedance (corresponding to the optimal Pout and PAE) of the output stage transistors. At 94 GHz, the PA achieves gain of 19.7 dB, Pout of 18.3 dBm, and PAE of 13%, one of the best results ever reported for a W-band PA.